Positional tracking: Difference between revisions
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{{see also|Tracking}} | {{see also|Tracking}} | ||
'''Positional tracking''' is a technology that allows a device to know its position relative to the environment around it. It uses a combination of hardware and software to achieve the detection of its absolute position. It is an essential technology for [[virtual reality]] (VR), making it possible to track movement with six [[degrees of freedom]] (6DOF).<ref name=”1”> StereoLabs. Positional Tracking. Retrieved from https://www.stereolabs.com/documentation/overview/positional-tracking/introduction.html</ref><ref name=”2”> Lang, B. (2013). An introduction to positional tracking and degrees of freedom (DOF). Retrieved from http://www.roadtovr.com/introduction-positional-tracking-degrees-freedom-dof/</ref> | |||
Positional tracking is a technology that allows a device to | |||
Positional tracking is not the same as 3DOF head tracking. 3DOF head tracking only registers the rotation of the head ([[Rotational tracking]]), with movements such as pitch, yaw, and roll. Positional tracking registers the exact position and orientation of the headset in space, recognizing forward/backward, up/down and left/right movement <ref name=”3”> Rohr, F. (2015). Positional tracking in VR: what it is and how it works. Retrieved from http://data-reality.com/positional-tracking-in-vr-what-it-is-and-how-it-works</ref>. | |||
Positional tracking VR technology brings various benefits to the VR experience. It can change the viewpoint of the user to reflect different actions like jumping, ducking, or leaning forward; allow for an exact representation of the user’s hands and other objects in the virtual environment; increase the connection between the physical and virtual world by, for example, using hand position to move virtual objects by touch; and detect gestures by analyzing position over time <ref name=”2”></ref> <ref name=”4”> Boger, Y. (2014). Overview of positional tracking technologies for virtual reality. Retrieved from http://www.roadtovr.com/overview-of-positional-tracking-technologies-virtual-reality/</ref>. | Positional tracking VR technology brings various benefits to the VR experience. It can change the viewpoint of the user to reflect different actions like jumping, ducking, or leaning forward; allow for an exact representation of the user’s hands and other objects in the virtual environment; increase the connection between the physical and virtual world by, for example, using hand position to move virtual objects by touch; and detect gestures by analyzing position over time <ref name=”2”></ref> <ref name=”4”> Boger, Y. (2014). Overview of positional tracking technologies for virtual reality. Retrieved from http://www.roadtovr.com/overview-of-positional-tracking-technologies-virtual-reality/</ref>. | ||
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==Methods of positional tracking== | ==Methods of positional tracking== | ||
[[File:HMD and markers.png|thumb|1. Markers on | [[File:HMD and markers.png|thumb|1. Markers on a Sensics HMD (Image: www.roadtovr.com)]] | ||
[[File:Optical marker.png|thumb|2. Optical marker by Intersense (Image: www.roadtovr.com)]] | [[File:Optical marker.png|thumb|2. Optical marker by Intersense (Image: www.roadtovr.com)]] | ||
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Intersense, an American technology company, has developed successful acoustic tracking systems. | Intersense, an American technology company, has developed successful acoustic tracking systems. | ||
=== | ===Wireless tracking=== | ||
Wireless tracking uses a set of anchors that are placed around the perimeter of the tracking space and one or more tags that are tracked. This system is similar in concept to GPS, but works both indoors and outdoors. Sometimes referred to as indoor GPS. The tags [[triangulation (computer vision)|triangulate]] their 3D position using the anchors placed around the perimeter. A wireless technology called Ultra Wideband has enabled the position tracking to reach a precision of under 100 mm. By using sensor fusion and high speed algorithms, the tracking precision can reach 5 mm level with update speeds of 200 Hz or 5 ms [[Latency (engineering)|latency]]. | |||
<ref name=”6”> IndoTraq. Positional Tracking. Retrieved from http://indotraq.com/?page_id=122</ref> | |||
<ref name=”7”> Hands-On With Indotraq. Retrieved from https://www.vrfocus.com/2016/01/hands-on-with-indotraq/</ref> | |||
<ref name=”8”> INDOTRAQ INDOOR TRACKING FOR VIRTUAL REALITY. Retrieved from https://blog.abt.com/2016/01/ces-2016-indotraq-indoor-tracking-for-virtual-reality/</ref> | |||
Inertial tracking is made possible by the use of accelerometers and gyroscopes. Accelerometers measure linear acceleration, which is used to calculate velocity and the position of the object relative to an initial point. This is possible due to the mathematical relationship between position over time and velocity, and velocity and acceleration (4). A gyroscope measures angular velocity. It is a solid-state component based on microelectromechanical systems (MEMS) technology and operates based on the same principles as a mechanical gyro. From the angular velocity data provided by the gyroscope, angular position relative to the initial point is calculated. | ===Inertial tracking=== | ||
Inertial tracking is made possible by the use of accelerometers and gyroscopes, commonly bundled together in chips called [[IMU]]s. Accelerometers measure linear acceleration, which is used to calculate velocity and the position of the object relative to an initial point. This is possible due to the mathematical relationship between position over time and velocity, and velocity and acceleration (4). A gyroscope measures angular velocity. It is a solid-state component based on microelectromechanical systems (MEMS) technology and operates based on the same principles as a mechanical gyro. From the angular velocity data provided by the gyroscope, angular position relative to the initial point is calculated. | |||
This technology is inexpensive and can provide high update rates as well as low latency. On the other side, the calculations (i.e. integration and double-integration) of the values given by the accelerometers (acceleration) and gyroscope (angular velocity) that lead to the object’s position can result in a significant drift in position information - decreasing this method’s accuracy. | This technology is inexpensive and can provide high update rates as well as low latency. On the other side, the calculations (i.e. integration and double-integration) of the values given by the accelerometers (acceleration) and gyroscope (angular velocity) that lead to the object’s position can result in a significant drift in position information - decreasing this method’s accuracy. | ||
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In a controlled environment, magnetic tracking’s accuracy is good. However, it can be influenced by interference from conductive materials near the emitter of sensors, from other magnetic fields generated by other devices and from ferromagnetic materials in the tracking area. | In a controlled environment, magnetic tracking’s accuracy is good. However, it can be influenced by interference from conductive materials near the emitter of sensors, from other magnetic fields generated by other devices and from ferromagnetic materials in the tracking area. | ||
The [[ | The [[Razer Hydra]] motion controllers is an example of implementation of this specific type of positional tracking in a product. | ||
Most [[Head-mounted display|Head-mounted displays]] (HMDs) and smartphones contain [[IMUs]] or [[magnetometer|magnetometers]] that detect the magnetic field of Earth. | Most [[Head-mounted display|Head-mounted displays]] (HMDs) and smartphones contain [[IMUs]] or [[magnetometer|magnetometers]] that detect the magnetic field of Earth. | ||
Magnetic tracking can be AC or DC. Magnetic tracking is great because it doesn't need a Kalman filter. It is much higher quality than all other tracking methods, but there are constraints on its usage, like how it cannot be used in environments with a lot of metal due to interference. | |||
===Optical Tracking=== | ===Optical Tracking=== | ||
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'''[[Markerless tracking]]''' - tracking system that does not use [[fiducial markers]]. | '''[[Markerless tracking]]''' - tracking system that does not use [[fiducial markers]]. | ||
'''[[Markerless inside-out tracking]]''' | '''[[Markerless inside-out tracking]]''' - combines markerless tracking with inside-out tracking | ||
'''[[Markerless outside-in tracking]]''' - combines markerless tracking with outside-in tracking | |||
==Comparison of | ==Comparison of tracking systems== | ||
{{see also|Comparison of tracking systems}} | {{see also|Comparison of tracking systems}} | ||
{{:Comparison of tracking systems}} | {{:Comparison of tracking systems}} | ||